Information transfer and antipredator maneuvers in schooling herring

Abstract

Schooling behavior in fish has been recognized to confer antipredator advantages. However, the mechanisms that lead to various patterns of escape maneuvers in fish schools are largely unknown. Here, we investigated the effect of startle stimulus characteristics (distance and orientation) on the escape maneuvers of schools of a highly gregarious fish species, the Atlantic herring Clupea harengus. We quantified information transfer of the onset of startle responses by analyzing the speed of the waves of their propagation ( Uw = 6.7 ± 1.6 m/s; mean ± SD). Uw was found to be positively correlated with the number of early responders (i.e., individuals reacting with a latency <50 ms). In addition, we identified the rules determining two different evading maneuvers: highly aligned maneuvers (i.e., all individuals oriented in a relatively uniform direction) and “split” maneuvers (i.e., individuals escaping with low directional uniformity). The pattern of escape maneuvers was dependent on stimulus direction (αs). Lateral stimulation (30° < αs < 120°) elicits highly aligned maneuvers away from the stimulus, while frontal stimulations (αs < 30°) causes split maneuvers, which are followed by realignment about 1 s after stimulation. These simple rules suggest that certain stimulus characteristics are important factors determining the variability of antipredator maneuvers observable in schooling fish.